Dual supply voltages converter and method

ABSTRACT

A dual supply voltages converter divides a supply voltage by a constant to produce a feature voltage larger than one when the supply voltage is a first voltage and smaller than 1 when the supply voltage is a second voltage and squares the feature voltage for comparing with itself. After squared, a value larger than one will larger than itself and a value small than 1 will smaller than itself. As a result, the supply voltage is determined to be the first or second voltage and thereby to be converted to the desired output voltage.

FIELD OF THE INVENTION

[0001] The present invention relates generally to a voltage converter,and more particularly to a circuit and method to convert dual supplyvoltages to single supply voltage.

BACKGROUND OF THE INVENTION

[0002] The dual supply voltages operationable circuit is the trend ofthe integrated circuit (IC) design, and more and more circuit aredesigned for normally operating with dual supply voltages even multiplesupply voltages. Therefore, the application of supply voltage conversioncircuit is quite popular, such as communication, wireless local areanetwork (WLAN), analog-to-digital circuit in optical fibercommunications, digital video disc (DVD), liquid crystal display (LCD)driving circuit, motherboard, central processing unit (CPU), generallyconsumer electronic apparatus, or consumer integrated circuit all needthis kind of conversion circuit. Hence, if such conversion circuit issuccessfully designed and produced, it will bring unlimited trade.

[0003] In many IC design, the designed circuit must be operated underdifferent supply voltages at the same time, and the external conversioncircuit must be modified without changing the internal supply voltageand design of the circuit. Designing a dual supply voltages converter isexpected for connecting the available supply voltage from external tocore circuit, and, for example, typically 5V and 3.3V are successfullyconverted to 3.3V for internal circuit. Accordingly, the designedcircuit will be competitive and tradable.

[0004] However, in the current IC design, a bandgap reference circuit orthe traditional converter circuit is used in the most design of the dualsupply voltages converter. In using bandgap reference circuit, thedifference of the provided supply voltages cannot be too large such as afew hundreds of milivolts, and in using traditional converter circuit,the volume of whole circuit will be quite huge and cannot be integrated.

SUMMARY OF THE INVENTION

[0005] One object of the present invention is to design a new andpractical supply voltage converter with a new concept, which means todesign a dual supply voltages converter without changing the supplyvoltage and design of the core circuit to connect the supply voltagefrom external to core circuit, and no matter how much the inputtedsupply voltage is, it can be converted to a voltage with fixed outputvalue and provided to the core circuit.

[0006] Accordingly, a dual supply voltages converter includes an input,a control signal generator and an output circuit. The input is connectedwith a supply voltage at a first or a second voltage, and the firstvoltage is larger than the second one; the control signal generator isconnected to the input and generates a control signal in accordance withthe supply voltage as the first or second voltage. The control signal isat a first logic state when the supply voltage is the first voltage, andat a second logic state when the supply voltage is the second voltage;the output circuit includes a first and a second paths each connectedbetween the input and an output, and the two paths are switched by thecontrol signal. When the control signal is at the first logic state, thefirst path is turned on and the first voltage is converted to a thirdvoltage on the output; when the control signal is at the second logicstate, the second path is turned on and the second voltage is convertedto the third voltage on the output. The inputted supply voltage atdifferent levels will be automatically identified and converted withdifferent ratio, and a fixed voltage or single supply voltage isoutputted to the core circuit.

[0007] In a preferred embodiment of the present invention, the controlsignal generator divides the inputted supply voltage by a constant toproduct a feature voltage. The feature voltage is larger than one whenthe supply voltage is the first voltage, and the feature voltage issmaller than one when the supply voltage is the second voltage. Then thefeature voltage is squared and compared with itself. After squared, avalue larger than 1 will be larger than itself, and a value smaller than1 will be smaller than itself. As a result, the supply voltage isdetermined to be the first or second voltage, and the output circuitdecides a proper conversion ratio and converts the supply voltage to thedesired output voltage.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The above and other objects, features and advantages of thepresent invention will become apparent to those skilled in the art uponconsideration of the following description of the preferred embodimentsof the present invention taken in conjunction with the accompanyingdrawings, in which:

[0009]FIG. 1 shows a scheme for the dual voltage converter according tothe present invention;

[0010]FIG. 2 is an embodiment for the control signal generator in thedual voltage converter of FIG. 1; and

[0011]FIG. 3 is an embodiment for the output circuit in the dual voltageconverter of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

[0012] The voltage converter is a circuit that converts severaldifferent supply voltages to a single supply voltage. With this circuitdesign, the application of the designed circuit will be more popular andcompetitive. The main object and function of the invention is to designa new dual voltages converter applied to the design of the integratedcircuit. An embodiment is shown hereinafter, in which several values andcircuits are designed for exemplary purpose, and various modificationsand variations can be made according to the present invention withoutdeparting from the scope or spirit of the present invention.

[0013]FIG. 1 is the scheme for the dual voltage converter according tothe present invention. An input 10 is connected with a dual voltageconverter 12 to provide a supply voltage at 5V or 3.3V. Whether the dualvoltages converter 12 is connected to 5V or 3.3V, the dual voltageconverter 12 generates an output 14 of 3.3V to provide to the corecircuit 16.

[0014] The main function of the dual voltage converter 12 is convertingtwo different provided supply voltages to a single supply voltage. Atfirst, the provided supply voltage is determined to be 5V or 3.3V, andthen the supply voltage is converted to the single voltage for the corecircuit 16 by a simple converter circuit. To determine the supplyvoltage connected to the dual voltages converter 12 is 5V or 3.3V, FIG.2 shows an embodiment 20 for the control signal generator in the dualvoltage converter 12 of FIG. 1. The input 10 is connected to a divisioncircuit 22 for the supply voltage Vdd to be divided by four to produce afeature voltage Ve, and the feature voltage Ve is squared by a squarecircuit 24 to provide a squared voltage Vs. The outputs of the divisioncircuit 22 and the square circuit 24 are connected to a comparator 26 tocompare the feature voltage Ve with the squared voltage Vs. The outputof the comparator 26 is connected to an inverter 28, and, as a result,the outputs of the inverter 28 and the comparator 26 provide a pair ofcomplementary control signals 30 and 32, by which the decision of thelogic states is further described in the following.

[0015] When the input 10 is connected with the supply voltage Vdd of 5V,the division circuit 22 produces the feature voltage $\begin{matrix}{{{Ve}\left( {5V} \right)} = {{Vdd} \div 4}} \\{= {5{V \div 4}}} \\{= {1.25{V.}}}\end{matrix}$

[0016] When the input 10 is connected with the supply voltage Vdd of3.3V, the division circuit 22 produces the feature voltage$\begin{matrix}{{{Ve}\left( {3.3V} \right)} = {{Vdd} \div 4}} \\{= {3.3{V \div 4}}} \\{= {0.825{V.}}}\end{matrix}$

[0017] In other words, the feature voltage Ve (5V) of the 5V supplyvoltage is larger than one, and the feature voltage Ve (3.3V) of the3.3V supply voltage is smaller than one.

[0018] Then, the feature voltage Ve is squared to produce a squaredvoltage Vs by a square circuit 24. The squared voltage of the featurevoltage Ve (5V) for the 5V supply voltage is $\begin{matrix}{{{Vs}\left( {5V} \right)} = (1.25)^{2}} \\{{= 1.5625},}\end{matrix}$ and Vs(5V) = 1.5625 > 1.25 = Ve(5V).

[0019] In contrast, the squared voltage of the feature voltage Ve (3.3V)for the 3.3V supply voltage is $\begin{matrix}{{{Vs}\left( {3.3V} \right)} = (0.825)^{2}} \\{{= {0.68V}},}\end{matrix}$ and Vs(3.3V) = 0.68 < 0.825 = Ve(3.3V).

[0020] In other words, the feature voltage Ve (5V) of the 5V supplyvoltage becomes larger after squared, and the feature voltage Ve (3.3V)of the 3.3V supply voltage becomes smaller after squared. Acharacteristic is used that a value larger than one gets greater aftersquared, and a value smaller than one gets smaller after squared. As aresult, the different supply voltages Vdd can be determined.

[0021] The output Vs of the square circuit 24 and the output Ve of thedivision circuit 22 are compared by the comparator 26 to provide thecomplementary control signals 30 and 32. If the voltage of the supplyvoltage Vdd is 5V, the squared voltage Vs (5V) is larger than thefeature voltage Ve (5V) and the logic states of the control signal 30and 32 are

[0022] A=0, and

[0023] B=1.

[0024] Contrarily, if the voltage of the supply voltage Vdd is 3.3V, thesquared voltage Vs (3.3V) is smaller than the feature voltage Ve (3.3V)and the logic states of the control signal 30 and 32 are

[0025] A=1, and

[0026] B=0.

[0027] The voltage of the supply voltage Vdd is thus determined and thecorresponding control signals 30 and 32 are provided according to thelevel of the supply voltage Vdd.

[0028] After determining the inputted supply voltage Vdd is 5V or 3.3V,the supply voltage Vdd is converted to the desired voltage. FIG. 3 showsthe embodiment 34 for the output circuit in the dual voltage converter12, which includes two paths arranged from the input 10 to the output42. The first path comprises a PMOS 36 and a voltage divider 40, and thesecond path comprises a PMOS 38. The control signals A and Baforementioned are connected to the gates of the PMOSes 36 and 38,respectively, and switch between the two paths to provide differentconversion ratio by switching the MOS switches 36 and 38. As foregoingmentioned, when the supply voltage Vdd is 5V, by the operation of thecontrol signal generator 20, A=0 and B=1, the PMOS 36 will be turned onand the PMOS 38 will be turned off. The 5V supply voltage Vdd isconverted to the output voltage Vout of 3.3V through the PMOS 36 anddivided by the resistors in the voltage divider 40 to provide to thecore circuit 44. On the other hand, when the supply voltage Vdd is 3.3V,by the operation of the control signal generator 20, A=1 and B=0, thePMOS 36 will be turned off and the PMOS 38 will be turned on. The 3.3Vsupply voltage Vdd is converted to the output voltage Vout of 3.3Vthrough the PMOS transistor 38 and connection to the output 42 toprovide to the core circuit 44. As a result, whether the supply voltageis 5V or 3.3V, the output 42 always provides fixed voltage 3.3V to thecore circuit 44.

[0029] The invented converter converts different supply voltages to asingle voltage by use of small circuit, and the circuit is achieved byCMOS process and is economic.

[0030] While the present invention has been described in conjunctionwith preferred embodiments thereof, it is evident that manyalternatives, modifications and variations will be apparent to thoseskilled in the art. Accordingly, it is intended to embrace all suchalternatives, modifications and variations that fall within the spiritand scope thereof as set forth in the appended claims.

What is claimed is:
 1. A dual supply voltages converter comprising: aninput for being connected with a supply voltage at a first voltage or asecond voltage smaller than the first voltage; a control signalgenerator connected to the input for generating a control signal at afirst logic state responsive to the first voltage and a second logicstate responsive to the second voltage; and an output circuit includinga first and a second paths each connected between the input and anoutput for being switched by the control signal to turn on the firstpath responsive to the first logic state to thereby transform the firstvoltage to a third voltage and to turn on the second path responsive tothe second logic state to thereby transform the second voltage to thethird voltage on the output.
 2. The converter of claim 1, wherein thecontrol signal generator comprises: a division circuit for dividing thesupply voltage by a constant to produce a feature voltage larger thanone when the supply voltage is the first voltage and smaller than 1 whenthe supply voltage is the second voltage; a square circuit for squaringthe feature voltage to produce a squared voltage; and a comparator forcomparing the feature voltage with the squared voltage to set thecontrol signal to the first logic state when the squared voltage islarger than the feature voltage and to the second logic state when thesquared voltage is smaller than the feature voltage.
 3. The converter ofclaim 1, wherein the first path includes a MOS with a gate connected tothe control signal to turn on the first path.
 4. The converter of claim1, wherein the first path includes a voltage divider to produce thethird voltage from the first voltage.
 5. The converter of claim 2,further comprising an inverter connected with the control signal toproduce a complementary signal connected to the output circuit.
 6. Theconverter of claim 5, wherein the second path includes a MOS with a gateconnected to the complementary signal to turn on the second path.
 7. Theconverter of claim 1, wherein the third voltage equals to the secondvoltage.
 8. A method for converting dual supply voltages to singlesupply voltage, the method comprising the steps of: inputting a supplyvoltage at a first voltage or a second voltage smaller than the firstvoltage; generating a control signal at a first logic state responsiveto the first voltage and a second logic state responsive to the secondvoltage; and switching by the control signal to turn on a first pathresponsive to the first logic state to thereby transform the firstvoltage to a third voltage and to turn on a second path responsive tothe second logic state to thereby transform the second voltage to thethird voltage.
 9. The method of claim 8, wherein the generating acontrol signal comprises the steps of: dividing the supply voltage by aconstant to produce a feature voltage larger than one when the supplyvoltage is the first voltage and smaller than 1 when the supply voltageis the second voltage; squaring the feature voltage to produce a squaredvoltage; and comparing the feature voltage with the squared voltage toset the control signal to the first logic state when the squared voltageis larger than the feature voltage and to the second logic state whenthe squared voltage is smaller than the feature voltage.
 10. The methodof claim 8, further comprising connecting a MOS in the first path toturn on the first path by switching the MOS by the control signal. 11.The method of claim 8, wherein the first voltage is divided to producethe third voltage when the first path is turn on.
 12. The method ofclaim 8, further comprising inverting the control signal to produce acomplementary signal.
 13. The method of claim 12, further comprisingconnecting a MOS in the second path to turn on the second path byswitching the MOS by the complementary signal.